The long term goal of this project is to identify mechanisms involved with human cytomegalovirus (HCMV) acceleration of transplant vascular sclerosis. The primary cause of graft loss of all vascularized organ transplants is due to a vascular lesion associated with chronic rejection. This form of vasculopathy referred to as TVS is characterized by concentric neointimal smooth muscle cell proliferation that results in vessel occlusion and ultimately graft failure. To date the only therapy available to treat severe TVS is retransplantation. Clinical studies in transplant recipients have demonstrated a direct link between HCMV and the acceleration of TVS. Based on these findings, we have developed a rat model of heart and small bowel transplantation in which CMV infection accelerates the time and severity of TVS. While the exact mechanism through which CMV mediates this process is unknown, recent work from our group suggests that CMV may contribute to TVS through induction of smooth muscle cell (SMC) migration towards sites of chemokine production through expression of a virally encoded chemokine receptor (US28). We have also observed that Rat and Murine CMV also induce SMC migration through their respective viral chemokine receptors R33 and M33, which are functional homologues of HCMV US28. We hypothesize that the mechanism of CMV-accelerated TVS involves the expression of virally encoded chemokine receptors leading to intimal SMC migration, which results in the characteristic vascular lesions of TVS. Therefore, we will utilize our in vitro and in vivo models to extend our observations and determine the role of virally encoded chemokine receptors in the development of TVS in three specific aims. First, using a rat cardiac transplant model of chronic rejection, we will determine the effects of virus on the kinetics of disease progression of TVS and the extent of viral expression in tissues as well as the cell types involved in the process. We will also determine the host factors such as chemokines and cytokines, and the contribution of R33 involved at various stages of the development of RCMV-induced TVS. Secondly, we will characterize the R33 domains involved in signaling which induce SMC migration and the ligands, which serve as agonists or antagonists to induced cellular movement. In the last specific, we will generate recombinant RCMV which contain mutations in domains involved in signaling to understand their contribution to TVS in the rat cardiac transplant model. Lastly, antagonists of R33 induced SMC migration in vitro will be tested for their ability to block TVS in the in vivo rat model. These studies will provide a valuable animal model to understand the role of CMV in the acceleration of TVS. In addition completion of these studies will form the basis for novel and rational design of therapeutic strategies to enhance long-term graft survival in HCMV infected transplant recipients.